I had one come from a headhunter recently. One who didn't sound too professional but was marketing a specific upper management job that had been advertised.
Just tried dialing this number with my Vonage VoIP line and got the following message (the number that this "out of service" number is dialing is my Bell Canada landline):
You have just dialed a number that is not in use. Please check your directory or dial zero for assistance. Thank you for using Allstream.
My brother was trying to call me from New York using Skype. He called twice, but both times I didn't hear anything on the line. Looks like the Skype service doesn't work very well.
I answered, and the caller claimed to be Emmanuel from something or other Air Duct Cleaning Services. I informed him that I was on the Do Not Call Registry and that the call was illegal, then hung up.